This is a relatively confusing scenario, so I will try to lay it out as clearly as possible.

My family is currently staying with my uncle at his bach. He has a phoneline there, administered by Telecom, and connected to broadband, on a very small account. We were going to be staying here for an extended period of time, and would be using quite a lot of data, and so we thought we would try using our home internet connection, since it is not in use at home while we are away. This is administered by Telstraclear. We weren't sure it would work, but we figured we'd try and see.

A new modem was purchased, (TP-Link WD8960N), so there is no issue with hangover of old settings. This was configured with our TelstraClear settings, and to our great delight, it seemed to connect and work no problem.

This was 6 months ago.

This Christmas, the same scenario occurred, so we got that modem out (the settings in it had not been touched, it had just been off for a few months), plugged it in, and we were away.

Today, my uncle received an email from Telecom, informing him that he had used 80% of his data cap - a huge surprise to us, as we didn't believe his modem (with his username and password) was in use at all.

I logged into the modem, but unfortunately, I assume as a security measure, the modem doesn't allow you to see what username/password it's using to connect to the ISP. I reentered the TC username and password, and rebooted the router. The external IP address now certainly seems to be from TC (203.97.210.xxx). Unfortunately, stupidly, I forgot to check what it was before I reset the settings.

It has been the best part of 10 years since I have worked in tech, so things may have changed. Does it actually now not matter what username and password are in the modem, and is it somehow just charged to whatever account is in charge of the phone line? Could the modem somehow have received "updated" ISP details from the cabinet or ISP? Is it likely to be working ok now, and I just have to check it each time the modem reboots? Is it possible to be connected through a TelstraClear gateway, with TelstraClear usernames and passwords, and for the data to be being applied to a Telecom account? It appears, over the past few days, that there has been no usage applied to the TC account at all.

I realise this is confusing, I am happy to try to clarify anything further that I can.

Fascinating, and thanks for the reply. I guess that explains it. Although it raises the massive question of why you have to enter a username and password into the router still. Or is that just so that it is backwards compatible?

Ok, back to the drawing board, I guess. Now I have to work out the most economic way of having 2 months ish of relatively high usage (20-30GB per months), and probably <2GB usage every other month. Probably with Telecom, unless I can convince him to change providers. Bugger.

When on holiday you should have to consider changing some habits - scale down on the file sharing for example, make sure online backups are not running, etc... Specially when using someone else's account.

Not doing any of that, but I am working - RDP into 2 different computers, most of the time. And I don't have anyone I can on-charge the cost to. Plus there are 10-12 people using the account on a daily basis through the wifi. No filesharing, but standard daily use.

We're looking at that option at the moment. Not sure how easy downgrading is after a month or so, though, plus he has a legacy tolls package that they don't seem to offer any more. Gets more complicated by the minute. But we're looking at options.

Back to the original question, it depends on the ISP. As noted, Telecom ignores the username and password so any modem connected to a Telecom line will charge to that line.

TelstraClear does use the username and password. If "User A", a TelstraClear customer, uses their username and password while connected to User B's line (where User B is also with TelstraClear), then the usage is charged to User A.

markboynz: We're looking at that option at the moment. Not sure how easy downgrading is after a month or so, though, plus he has a legacy tolls package that they don't seem to offer any more. Gets more complicated by the minute. But we're looking at options.

Just get an extra Naked DSL plan from another provider with no contract. Keep it for a couple of months then cancel or get a better plan than the Telecom plan they are on in the first place then everyone is happy.

markboynz: But given the previous response, if I got an "extra" naked dsl package from someone else, surely it's still going to be applied to the original Telecom account, given the problems we've already had?

No its another totally different line so will have nothing to do with Telecom.

Behodar: Back to the original question, it depends on the ISP. As noted, Telecom ignores the username and password so any modem connected to a Telecom line will charge to that line.

TelstraClear does use the username and password. If "User A", a TelstraClear customer, uses their username and password while connected to User B's line (where User B is also with TelstraClear), then the usage is charged to User A.

If your Uncle does change to Telstra then your modem settings from home would work so thats an option.